Electromagnetic wave energy seal

ABSTRACT

An improved electromagnetic wave energy seal for microwave ovens which incorporates a continuous capacitive-type seal that cooperates with a continuous choke-type seal for preventing the escape of electromagnetic wave energy from the cavity of such microwave ovens. The capacitive-type seal is a flexible seal plate which abuts the surface defining the opening of the cavity of the microwave oven, and the choke-type seal is an irregularly shaped piece of dielectric material located within a metallic housing and having a concave portion which allows entry therein of the perimeter of the flexible seal plate.

United States Patent [191 51 May 29, 1973 Jarvis [54] ELECTROMAGNETIC WAVE ENERGY SEAL [75] Inventor: George A. Jarvis, Minneapolis,

Minn.

[73] Assignee: Litton Systems, Inc., Beverly Hills,

\ Calif.

[22] Filed: Nov. 15, 1971 [21] Appl No.: 198,803

[52] U.S. Cl ..2l9/l0.55 [51 1 Int. Cl. .H05b 9/06 [58] Field of Search ..2l9/l0.55

[56]v References Cited UNITED STATES PATENTS 3,633,564 1/1972 Togashi 2l9/10.55

Primary Examiner-J. V. Truhe Assistant ExaminerHugh D. Jaeger Attorney-Franklin D. Jankosky [57] ABSTRACT 15 Claims, 4 Drawing Figures Patented May 29, 1973 GEORGE A. JARV/S INVENTOR B271 [a i ATXRNE'YJ ELECTROMAGNETIC WAVE ENERGY SEAL FIELD OF THE INVENTION This invention relates to microwave ovens and more particularly to a novel door seal for preventing the escape'of electromagnetic wave energy from such ovens.

DESCRIPTION OF THE PRIOR ART The typical microwave oven includes a cavity wherein foodstuffs may be placed to be cooked by exposing the foodstuffs to electromagnetic wave energy radiated by a magnetron. As a practical matter, access must be provided to facilitate the insertion and the removal of the foodstuffs to and from the cavity of the microwave oven. Pivotally supported doors have been generally utilized to provide such access. As one would expect, electromagnetic wave energy in the vicinity of the perimeter of the door will escape from the cavity of the microwave oven unless proper measures are taken to block such escape of electromagnetic wave energy.

In the past, microwave oven manufacturers have utilized various types of electromagnetic wave energy seals to prevent the escape of electromagnetic wave energy from the cavity of the microwave oven. Originally, microwave ovens featured direct metallic contact between the inside surface of a metallic door and the front surface of a metallic housing, with the addition of spring biasing of the door to maintain contact between the two surfaces. However, the spring biasing method did not prove satisfactory over an extended period of use because of warping of the metallic surfaces or because of deterioration of the springs. In either case, arcing between the respective surfaces of the door and the housing and subsequent excessive leakage of electromagnetic wave energy occurred unless proper maintenance procedures were strictly observed.

Subsequent approaches included the insertion of a number of non-metallic spacers or a conductive rubber gasket between the door and the microwave oven housing to establish a gap so as to prevent arcing of the electromagnetic wave energy. Usually these approaches included a recessed area having a terminating conducting surface located an integral number of one-half wave lengths of the fundamental frequency of the magnetron from the origin of the gap, or included a series of recessed areas having a depth equal to approximately one-quarter wave length of the fundamental frequency of the magnetron. In some instances, such recessed areas have been made smaller and have been filled with a dielectric material to maintain the same. electrical wave length, but allowed'the electromagnetic wave energy seal to be more compact. While these prior electromagnetic wave energy seals were originally acceptable, the recently adopted standards of the Department of Health, Education and Welfare requiring all microwave ovens to have a radiation leakage level of less than I mw./cm upon sale and being capable of maintaining a radiation leakage level of less than 5 mw./cm under all operating conditions preclude many such electromagnetic wave energy seals from being utilized in microwave ovens sold in the United States.

On the other hand, effective electromagnetic wave energy seals have been constructed within such standards, for example, a seal has been constructed utiliz' ing both dielectric material and ferrite material to respectively attenuate and absorb electromagnetic wave energy. However, the cost of such a seal is too expensive for most applications, for example, for private consumer microwave ovens.

Accordingly, it is an object of the present invention to provide an improved electromagnetic wave energy seal which substantially eliminates the arcing of electromagnetic wave energy in proximity of the door.

It is a further object of the present invention to provide an improved electromagnetic wave energy seal which is within the standards set by the Department of Health, Education and Welfare of the United States Government.

It is a still further object of the present invention to provide an improved electromagnetic wave energy seal which is not dependent entirely upon the biasing of a spring-loaded door to maintain contact between the interior surface of the door and the front surface of the microwave oven housing.

It is another object of the present invention to provide an improved electromagnetic wave energy seal which is effective and inexpensive.

SUMMARY OF THE INVENTION In accordance with the objects set forth above, the present invention provides an improved electromagnetic wave energy seal for preventing the escape of electromagnetic wave energy from the cavity of microwave ovens. The electromagnetic wave energy seal comprises a continuous choke-type seal that includes an irregularly-shaped piece of dielectric material located within a metallic housing and having a concave portion, and a capacitive-type seal which is a flexible seal plate that abuts the surface defining the opening of the cavity of the microwave oven. The perimeter of the flexible seal plate is curved inwardly toward the microwave oven door and is adapted to enter the concave portion of the dielectric material when the door is closed. The continuous choke-type seal primarily prevents the escape of the fundamental frequency of the electromagnetic wave energy and the capacitive-type seal primarily prevents the escape of the harmonic frequencies of the electromagnetic wave energy.

BRIEF DESCRIPTION OF THE DRAWINGS Additional objects, advantages and characteristic features of the present invention will become readily apparent from the following detailed description of the preferred embodiments of the invention when taken in conjunction with the drawings in which:

FIG. 1 is a perspective view of a microwave oven in accordance with the present invention;

FIG. 2 is the interior side of the microwave oven door in accordance with the present invention;

FIG. 3 is a cross-sectional view of the electromagnetic wave energy seal taken along line 3-3 of FIG. 2 in accordance with the present invention; and

FIG. 4 is an enlarged functional diagram of the electromagnetic wave energy seal, including the cooking cavity of the microwave oven, in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown a perspective view of a microwave oven 10 in accordance with the principles of the present invention. As is well known, foodstuffs may be placed within a closed cavity to be cooked by the electromagnetic wave energy generated by a magnetron. While the present invention will be described with reference to such cooking by means of a magnetron operating at 2,450 MHz, it should be understood that the principles of the electromagnetic wave energy seal taught by the present invention are not limited to any particular frequency.

The exterior of the microwave oven is generally comprised of a housing 11, a door 12 and a control panel 15. The control panel 15 includes a conventional timer and an indicator light. The door 12 includes a window 14 consisting of an RF screen sandwiched between two panes of glass which enable one to view the cooking of the foodstuffs placed within the cavity of the microwave oven 10. The handle 13 allows one to open and close the door 12.

Referring now to FIG. 2, there is shown the interior side of the microwave oven door 12 in accordance with the principles of the present invention. The interior side of the door 12 is principally comprised of an interior housing panel 16, a choke 22, a flexible seal plate 24 and the window 14. The following illustrated parts of the microwave oven 10 will be briefly described since they are not directed toward the electromagnetic wave energy seal of the present invention. The door 12 may be rotatably supported by means of a pair of hinges 17A and 17B which are respectively located in the openings 18A and 18B of the interior housing panel 16. An opening 19 in the interior housing panel 16 is for attaching one end of a suitable member (not shown) to the door 12. Such suitable member is for restricting the swing of the door 12. Further shown is a pair of latching means 20A and 20B, which respond to the movement of the handle 13. The latching means 20A and 20B are respectively located in the openings 21A and 21B of the interior housing panel 16. The interior housing panel 16 further includes a concave portion 16C which allows air to be expelled from the cavity of the microwave oven 10.

Referring now to both FIGS. 2 and 3, there are shown the components which comprise the electromagnetic wave energy seal of the present invention. The choke 22 is'comprised of a continuous piece of suitable dielectric material 23, such as polypropyleyne, and a recessed area or cavity 168 that extends around the approximate perimeter of the door 12 in which the dielectric material 23 is located. As is well known, a choke may be comprised of a smaller recessed area or cavity that is filled with suitable dielectric material to be the electrical equivalent of a larger recessed area or cavity. As clearly shown in FIG. 3, the piece of dielectric material 23 is of irregular shape and includes a protruding portion 23A and a concave portion 238; The protruding portion 23A has a lip which provides a sanitary seal to prevent foreign particles from entering the recessed area 168. The primary purpose of the choke 22 is to prevent the escape from the microwave oven 10 of the electromagnetic wave energy of the fundamental frequency of 2,450 MHz. Further shown is the flexible seal plate 24 which is a picture frame shaped sheet of metallic material having an opening as illustrated to accommodate the window 14. The flexible seal plate 24 may be properly aligned on the door 12 by means of a plurality of studs 24A that are welded on the flexible seal plate 24 and which pass through a respective plurality of openings 16A of the interior housing panel 16. The flexible seal plate 24 may be secured to the interior housing panel 16 by means of fastening a plurality of nuts 27 to the respective plurality of studs 24A. The outside perimetric edge 24B of the flexible seal plate 24 is bent inwardly toward the interior housing panel 16 to facilitate its entry into the concave portion 238 of the piece of dielectric material 23.

While the cooking cavity 26 is not shown in its entirety, a typical cooking cavity is defined by five conductive walls of suitable metallic material and the interior surface of a microwave oven door in its closed position. One such conductive wall is illustrated by the numeral designated 25A. The numeral 258 designates the front surface which defines the opening of the cavity 26 of the microwave oven 10. As illustrated in FIG. 3, a portion of the flexible seal plate 24 abuts the front surface housing 253. Either the front surface 25B or the flexible seal plate may be painted with a thin layer of dielectric material to further prevent arcing of the electromagnetic wave energy. The resulting contact area between the flexible seal plate 24 and the front surface 25B forms an effective capacitive seal to prevent the escape from the microwave oven 10 of the electromagnetic wave energy of the harmonics of the fundamental frequency, principally the electromagnetic wave energy of the 4,900 MHz and 7,350 MHz harmonics. The outside perimetric edge 24B is bent inwardly toward the interior housing panel 16 to eliminate arcing which has occurred in other microwave ovens utilizing the common capacitive seal which features direct contact along the entire abutting surfaces, as illustrated in US. Pat. No. 2,956,143 issued Oct. 1 l, 1960 to L. H. Schall.

Referring now to FIG. 4, there is shown an enlarged functional diagram of one corner of the electromagnetic wave energy seal, including the cooking cavity of the microwave oven, in accordance with the present invention. The primary purpose of FIG. 4 is to illustrate one of the embodiments of the present invention, namely, the use of an electromagnetic wave energy seal having rounded corners for use in a microwave oven wherein the cooking cavity has molded rounded corners. The solid and dashed lines 23C and 23C respectively define one of the four corners of the continuous piece of dielectric material 23 of the choke 22. The line 24C defines the rounded outside corner of one of the four corners of the flexible seal plate 24. The dashed line 25C defines the rounded corner of one of thefour rounded corners that describe the boundary of the access opening of the cooking cavity 26. It has been found by experiment that the electromagnetic wave energy seal of the present invention is more effective if the four corners of such seal are rounded and aligned with the rounded corners of the cooking cavity. However, it should be understood that theabove-described electromagnetic wave energy seal is not limited toa capacitive-type seal and choke-type seal combination wherein the corners of the seals or the cooking cavity are rounded. It should be further understood that the electromagnetic wave energy seal of the present invention is not limited to any specific dimensions, but is meant to include the combination of a capacitive-type seal cooperating with a choke-type seal to effectively prevent the escape from the microwave oven of the fundamental and harmonic frequencies of electromagnetic wave energy.

Thus, although the present invention has been shown and described with reference to particular embodiments, for example, a choke seal of polypropylene,

nevertheless, various changes and modifications obvious to a person skilled in the art to which the invention pertains, for example, a choke seal of other suitable dielectric material, are deemed to lie within the spirit, scope and contemplation of the invention as set forth in the appended claims.

What is claimed is:

1. Microwave oven apparatus comprising:

a housing having a cooking cavity located therein, said housing having a surface with an opening therein which defines an access opening for said cooking cavity to permit foodstuffs to be placed in said cooking cavity;

means for supplying electromagnetic wave energy to said cooking cavity;

a movable door mounted to said housing and adapted to be placed over said access opening of said cooking cavity to complete an enclosed cooking cavity, said movable door including means for preventing the escape of said electromagnetic wave energy from said cooking cavity, said means comprised of continuous choke-type seal means located in proximity to the perimeter of said access opening of said cooking cavity and capacitive-type seal means adapted to abut said surface of said housing and extend into said continuous choke-type seal means when said movable door is placed over said access opening of said cooking cavity;

said access opening of said cooking cavity is of a general rectangular shape;

said continuous choke-type seal means is comprised of a general rectangularly shaped metallic recessed channel which is substantially filled with a dielectric material; and

said capacitive-type seal means is a flexible metallic plate having an outside perimeter which extends into said recessed channel when said movable door is placed over said access opening of said cooking cavity.

2. Microwave oven apparatus as recited in claim 1 wherein:

said means for supplying electromagnetic wave energy to said cooking cavity is a magnetron having a fundamental operating frequency of 2,450 megahertz;

said continuous choke-type seal means primarily prevents the escape of electromagnetic wave energy of the fundamental operating frequency from said cooking cavity; and

the capacitive-type seal means primarily prevents the escape of electromagnetic wave energy of the harmonics of the fundamental operating frequency from said cooking cavity.

3. Microwave oven apparatus as recited in claim 1 wherein:

said continuous choke-type seal means is comprised of a general rectangular shaped metallic recessed channel having an open side, and said dielectric material is of irregular shape and includes a concave portion; and

said outside perimeter of said flexible metallic plate extends into said open side of said recessed channel and said concave portion of said irregularly shaped piece of dielectric material when said movable door is placed ov'er'said access opening of said cooking cavity.

4. Microwave oven apparatus as recited in claim 2 wherein said irregularly shaped piece of dielectric material of said continuous choke-type seal means includes a continuous lip portion for preventing foodstuffs from entering said metallic recessed channel.

5. Microwave oven apparatus as recited in claim 1 wherein:

said flexible metallic plate of said capacitive-type seal means forms a continuous effective metallic contact with said surfaceof said housing;

said outside perimeter of said flexible metallic plate is partially bent inwardly toward said movable door; and

said flexible seal plate is mounted to said movable door by means of a plurality of studs located at a sufficient distance from said outside perimeter of said flexible seal plate to allow said outside perimeter to extend into said recessed channel of said capacitive-type seal means when said movable door is placed over said access opening of said cooking cavity.

6. Microwave oven apparatus as recited in claim 5 wherein said portion of said flexible seal plate abutting said surface of said housing forms an effective capacitive seal and said inwardly bent portion of said outside perimeter of said flexible seal plate prevents arcing of electromagnetic wave energy.

7. Microwave oven apparatus as recited in claim 1 wherein said continuous choke-type seal means is of a picture frame shape wherein the inside perimeter of said choke-type seal means is of a smaller length than the perimetric lengthof said access opening of said cooking cavity and the outside perimeter of said choketype seal means is of a larger length than said perimetric length of said access opening of said cooking cavity.

8. Microwave oven apparatus as recited in claim 1 wherein:

said access opening of said cooking cavity is of general rectangular shape and the corners of said access opening are rounded;

said continuous choke-type seal means is of a picture frame shape wherein the inner and outer perimeters of said picture frame shape correspond relatively to said general rectangular shape of said access opening, said inner and outer perimeter of said picture frame shape having respective rounded corners; and

said outside perimter of said capacitive-type seal means is of general rectangular shape relatively similar to said general rectangular shape of said access opening and the respective corners of said outside perimeter of saidcapacitive-type seal means are rounded. I

9. Microwave oven apparatus as recited in claim 3 wherein said dielectric material is polypropyleyne.

l0. Microwave oven apparatus comprising:

a housing having a cooking cavity locatedtherein, said housing having a front surface with an opening therein which defines an access opening for said cooking cavity;

means for supplying electromagnetic wave energy to said cooking cavity;

a door mounted on the front surface of the housing,

said door having an interior surface which completely encloses the access opening of the cooking cavity and extends over the front surface of the housing; and

means for preventing the escape of electromagnetic wave energy along the perimeter of the interior surface of said door which extends over the front surface of the housing, said means comprising a metallic recessed channel located on one of either the housing front surface or the door interior surface in proximity to the perimeter of said access opening and a flexible metallic plate mounted on said one surface extending about the perimeter of said access opening, said flexible plate resiliently contacting the other surface when said door is closed over said cooking cavity.

11. The invention of claim 10 wherein said recessed channel and flexible metallic plate are located on the interior surface of said door with said flexible metallic plate extending into said recessed channel when said door is closed over said cooking cavity.

12. The invention of claim 10 wherein said recessed channel is substantially filled with a dielectric material.

13. The invention of claim 11 wherein the portion of said flexible metallic plate that extends into said recessed channel is bent inwardly toward said channel to prevent arcing of electromagnetic energy.

14. The invention of claim 10 wherein the surface of said metallic plate that contacts said other surface when the door is closed is coated with a thin layer of dielectric material.

15. The invention of claim 10 wherein the portion of said other surface contacting said metallic plate is coated with a thin layer of dielectric material. 

1. Microwave oven apparatus comprising: a housing having a cooking cavity located therein, said housing having a surface with an opening therein which defines an access opening for said cooking cavity to permit foodstuffs to be placed in said cooking cavity; means for supplying electromagnetic wave energy to said cooking cavity; a movable door mounted to said housing and adapted to be placed over said access opening of said cooking cavity to complete an enclosed cooking cavity, said movable door including means for preventing the escape of said electromagnetic wave energy from said cooking cavity, said means comprised of continuous choketype seal means located in proximity to the perimeter of said access opening of said cooking cavity and capacitive-type seal means adapted to abut said surface of said housing and extend into said continuous choke-type seal means when said movable door is placed over said access opening of said cooking cavity; said access opening of said cooking cAvity is of a general rectangular shape; said continuous choke-type seal means is comprised of a general rectangularly shaped metallic recessed channel which is substantially filled with a dielectric material; and said capacitive-type seal means is a flexible metallic plate having an outside perimeter which extends into said recessed channel when said movable door is placed over said access opening of said cooking cavity.
 2. Microwave oven apparatus as recited in claim 1 wherein: said means for supplying electromagnetic wave energy to said cooking cavity is a magnetron having a fundamental operating frequency of 2,450 megahertz; said continuous choke-type seal means primarily prevents the escape of electromagnetic wave energy of the fundamental operating frequency from said cooking cavity; and the capacitive-type seal means primarily prevents the escape of electromagnetic wave energy of the harmonics of the fundamental operating frequency from said cooking cavity.
 3. Microwave oven apparatus as recited in claim 1 wherein: said continuous choke-type seal means is comprised of a general rectangular shaped metallic recessed channel having an open side, and said dielectric material is of irregular shape and includes a concave portion; and said outside perimeter of said flexible metallic plate extends into said open side of said recessed channel and said concave portion of said irregularly shaped piece of dielectric material when said movable door is placed over said access opening of said cooking cavity.
 4. Microwave oven apparatus as recited in claim 2 wherein said irregularly shaped piece of dielectric material of said continuous choke-type seal means includes a continuous lip portion for preventing foodstuffs from entering said metallic recessed channel.
 5. Microwave oven apparatus as recited in claim 1 wherein: said flexible metallic plate of said capacitive-type seal means forms a continuous effective metallic contact with said surface of said housing; said outside perimeter of said flexible metallic plate is partially bent inwardly toward said movable door; and said flexible seal plate is mounted to said movable door by means of a plurality of studs located at a sufficient distance from said outside perimeter of said flexible seal plate to allow said outside perimeter to extend into said recessed channel of said capacitive-type seal means when said movable door is placed over said access opening of said cooking cavity.
 6. Microwave oven apparatus as recited in claim 5 wherein said portion of said flexible seal plate abutting said surface of said housing forms an effective capacitive seal and said inwardly bent portion of said outside perimeter of said flexible seal plate prevents arcing of electromagnetic wave energy.
 7. Microwave oven apparatus as recited in claim 1 wherein said continuous choke-type seal means is of a picture frame shape wherein the inside perimeter of said choke-type seal means is of a smaller length than the perimetric length of said access opening of said cooking cavity and the outside perimeter of said choke-type seal means is of a larger length than said perimetric length of said access opening of said cooking cavity.
 8. Microwave oven apparatus as recited in claim 1 wherein: said access opening of said cooking cavity is of general rectangular shape and the corners of said access opening are rounded; said continuous choke-type seal means is of a picture frame shape wherein the inner and outer perimeters of said picture frame shape correspond relatively to said general rectangular shape of said access opening, said inner and outer perimeter of said picture frame shape having respective rounded corners; and said outside perimter of said capacitive-type seal means is of general rectangular shape relatively similar to said general rectangular shape of said access opening and the respective corners of said outside perimeter of said capacitive-type seal means are rOunded.
 9. Microwave oven apparatus as recited in claim 3 wherein said dielectric material is polypropyleyne.
 10. Microwave oven apparatus comprising: a housing having a cooking cavity located therein, said housing having a front surface with an opening therein which defines an access opening for said cooking cavity; means for supplying electromagnetic wave energy to said cooking cavity; a door mounted on the front surface of the housing, said door having an interior surface which completely encloses the access opening of the cooking cavity and extends over the front surface of the housing; and means for preventing the escape of electromagnetic wave energy along the perimeter of the interior surface of said door which extends over the front surface of the housing, said means comprising a metallic recessed channel located on one of either the housing front surface or the door interior surface in proximity to the perimeter of said access opening and a flexible metallic plate mounted on said one surface extending about the perimeter of said access opening, said flexible plate resiliently contacting the other surface when said door is closed over said cooking cavity.
 11. The invention of claim 10 wherein said recessed channel and flexible metallic plate are located on the interior surface of said door with said flexible metallic plate extending into said recessed channel when said door is closed over said cooking cavity.
 12. The invention of claim 10 wherein said recessed channel is substantially filled with a dielectric material.
 13. The invention of claim 11 wherein the portion of said flexible metallic plate that extends into said recessed channel is bent inwardly toward said channel to prevent arcing of electromagnetic energy.
 14. The invention of claim 10 wherein the surface of said metallic plate that contacts said other surface when the door is closed is coated with a thin layer of dielectric material.
 15. The invention of claim 10 wherein the portion of said other surface contacting said metallic plate is coated with a thin layer of dielectric material. 